Then there are the tests of climate changes themselves: how does a model respond to the addition
of aerosols in the stratosphere such as was seen in the Mt Pinatubo «natural experiment»?
In my mind, the most serious peril of sulfate geoengineering is one that stems from a problem that is not at all in dispute: the fact that the lifetime of CO2 in the atmosphere is centuries to millennia, whereas the lifetime
of aerosols in the stratosphere is at best a few years.
Some models include volcanic effects by simply perturbing the incoming shortwave radiation at the top of the atmosphere, while others simulate explicitly the radiative effects
of the aerosols in the stratosphere.
Not exact matches
The effect also illustrates one proposal for so - called geoengineering — the deliberate, large - scale manipulation
of the planetary environment — that would use various means to create such sulfuric acid
aerosols in the
stratosphere to reflect sunlight and thereby hopefully forestall catastrophic climate change.
Such sulfuric acid
aerosols are already responsible for the bulk
of nacreous clouds that form
in the polar
stratosphere; added particles would just amp up the natural process (although it might also amp up damage the ozone layer).
It's designed to track an
aerosol plume
in the
stratosphere at a height
of 70,000 feet.
In fact, the aerosol layer in the stratosphere, which is also composed of sulphur particles, seems to have become thicker in recent year
In fact, the
aerosol layer
in the stratosphere, which is also composed of sulphur particles, seems to have become thicker in recent year
in the
stratosphere, which is also composed
of sulphur particles, seems to have become thicker
in recent year
in recent years.
Some
of those gases
in the chimney system such as chlorofluorocarbons (found
in refrigerants and
aerosols) and bromine compounds (found
in products such as fire extinguishers) are man - made and can become trapped
in the
stratosphere, lingering there for years.
They fear that similar
aerosol already
in the northern
stratosphere, which came from the eruption
of Mount Pinatubo
in the Philippines
in June 1991, may cause a dramatic loss
of ozone
in the northern hemisphere next February or March.
Alcide di Sarra
of La Sapienza University
in Rome and colleagues from an Italian - Danish team found that the volcanic
aerosol from Mount Pinatubo penetrated the Arctic
stratosphere in relatively thin layers, at altitudes below 16 kilometres.
OMPS is a three - part instrument: a nadir mapper that maps ozone, SO2 and
aerosols; a nadir profiler that measures the vertical distribution
of ozone
in the
stratosphere; and a limb profiler that measures
aerosols in the upper troposphere,
stratosphere and mesosphere with high vertical resolution.
«And at the end
of the summer, the «lid» comes back down, which leaves
aerosols in the
stratosphere,» he explains.
The main removal process for
aerosols is related to rain and clouds, and up
in the
stratosphere there isn't any to speak
of.
Sulphur dioxide reacts with water vapour to form long - lived droplets (
aerosols)
of sulphuric acid, and about 10 million tons
of these droplets are known to have accumulated
in the
stratosphere as a result
of the eruption.
In this case, large amounts of sulphate aerosols (small particles) are injected into the stratosphere by large explosive eruptions (the most recent one being Mt. Pinatubo in 1991
In this case, large amounts
of sulphate
aerosols (small particles) are injected into the
stratosphere by large explosive eruptions (the most recent one being Mt. Pinatubo
in 1991
in 1991).
For example, they predicted the expansion
of the Hadley cells, the poleward movement
of storm tracks, the rising
of the tropopause, the rising
of the effective radiating altitude, the circulation
of aerosols in the atmosphere, the modelling
of the transmission
of radiation through the atmosphere, the clear sky super greenhouse effect that results from increased water vapor
in the tropics, the near constancy
of relative humidity, and polar amplification, the cooling
of the
stratosphere while the troposphere warmed.
Thus the changes
in the
stratosphere are basically a function
of the greenhouse gases, ozone levels and volcanic
aerosols there.
Rough calculations show if you drill about a dozen mine shafts as deep as possible into the thing, and plunk megaton nuclear bombs down there, and then fire them off simultaneously, you'll get a repeat
of the Long Valley Caldera explosion
of about 800,000 years ago — which coated everything east
of it with miles
of ash and injected a giant
aerosol cloud into the
stratosphere — the ash layer alone formed a triangle stretching from the caldera to Louisiana to North Dakota, including all
of Arizona and most
of Idaho and everything
in between — I bet that would have a cooling factor
of at least -30 W / m ^ 2 — and you could go and do the Yellowstone Plateau at the same time — geoengineering at its finest.
«Geoengineering» by reducing insolation with
aerosols in the
stratosphere will also reduce the effectiveness
of solar panels.
Since
aerosols last much longer
in the
stratosphere than they do
in the rainy troposphere, the amount
of aerosol - forming substance that would need to be injected into the
stratosphere annually is far less than what would be needed to give a similar cooling effect
in the troposphere, though so far as the stratospheric
aerosol burden goes, it would still be a bit like making the Earth a permanently volcanic planet (think
of a Pinatubo or two a year, forever).
If we would pump
aerosols in the
stratosphere to artificially cool the Earth and thereby compensate (part
of) the current climate warming, we would be permanently living under a slight sunshade.
After a large volcanic eruption, the layer
of sulfate
aerosols in the
stratosphere gets thicker, and we see,
in the historic record, that the Earth cools down
in response.
Not it is not similar because one event injected sulfate
aerosols into the
stratosphere where they stayed for years and affected the globe while the other («human particulates and
aerosol pollution») were produced
in the troposphere and have a residency time
in the atmosphere
of about 4 days and had only a regional effect.
One driver
of temperatures
in this region is the abundance and variability
of ozone, but water vapor, volcanic
aerosols, and dynamical changes such as the Quasi - Biennial Oscillation (QBO) are also significant; anthropogenic increases
in other greenhouse gases such as carbon dioxide play a lesser but significant role
in the lower
stratosphere.
In fact, the major effect of significant volcanic eruptions is cooling due to the sulfate aerosols that they release (although in order to have a significant cooling effect, the eruption has to be large enough that it injects the aerosols into the stratosphere where they can stay around longer... and it apparently helps if the eruption is reasonably near to the equator
In fact, the major effect
of significant volcanic eruptions is cooling due to the sulfate
aerosols that they release (although
in order to have a significant cooling effect, the eruption has to be large enough that it injects the aerosols into the stratosphere where they can stay around longer... and it apparently helps if the eruption is reasonably near to the equator
in order to have a significant cooling effect, the eruption has to be large enough that it injects the
aerosols into the
stratosphere where they can stay around longer... and it apparently helps if the eruption is reasonably near to the equator).
Here I summarize two recent papers that model solar radiation management: the practice
of offsetting global warming by partially blocking sunlight, whether by seeding clouds, adding sulfate
aerosols to the
stratosphere, or placing giant mirrors
in space.
«Since 1997, when Pinatubo's
aerosol settled out, the
stratosphere has been exceptionally clear... Half or more
of the warming since 1995 may due to the lack
of large volcanic eruptions... That's about 0.13 °C... The remaining climate change is presumably caused by other forces, such as solar variability, El Nino, Atlantic AMO warming
in 1995, lower Albedo and maybe even a little greenhouse gas.»
I consider it as very likely that the 20 year trends will still be statistically significant also
in three, five or ten years from now, unless there is some strong volcanic explosion that blows a lot
of reflecting
aerosols in the
stratosphere causing a temporary temperature dip, or some other cause the effect
of which is explainable within the framework
of current knowledge about the climate system, but as event not really predictable.
Stratospheric
aerosols affect the chemistry and transport processes
in the
stratosphere, resulting
in the depletion
of ozone (Brasseur and Granier, 1992; Tie et al., 1994; Solomon et al., 1996; Chipperfield et al., 2003).
However the models» simplified treatment
of aerosol microphysics introduces biases; further, they usually overestimate the mixing at the tropopause level and intensity
of meridional transport
in the
stratosphere (Douglass et al., 2003; Schoeberl et al., 2003).
Aerosols from volcanic eruptions do have a cooling effect once they reach the
stratosphere but the effect
of high wind speed
in the upper atmosphere would rapidly disperse these, and any local effects would be very slight.
Until the 1990s, the widespread use
of chlorofluorocarbons (CFCs) for refrigerants and
aerosols created an ozone hole
in the Earth's
stratosphere (the second layer
of the atmosphere from Earth's surface) over Antarctica.
Sulphate
aerosols in the
stratosphere (which were the main topic
of this piece and these Climate Feedback posts) and mirrors / refractors
in space (also
in that piece, and
in this paper by Roger Angel) both have the potential to provide as much by way
of negative forcing as a doubling
of CO2 provides by way
of positive forcing.
Ridley and his colleagues also tracked the source
of aerosols in the lower
stratosphere from volcanic eruptions during the 2000s.
One knob that we could control: The amount
of sulphate
aerosols in the
stratosphere.
Of course temperatures
in the troposphere is influenced by volcanic
aerosols in the troposphere and
stratosphere.
Although we focus on a hypothesized CR - cloud connection, we note that it is difficult to separate changes
in the CR flux from accompanying variations
in solar irradiance and the solar wind, for which numerous causal links to climate have also been proposed, including: the influence
of UV spectral irradiance on stratospheric heating and dynamic
stratosphere - troposphere links (Haigh 1996); UV irradiance and radiative damage to phytoplankton influencing the release
of volatile precursor compounds which form sulphate
aerosols over ocean environments (Kniveton et al. 2003); an amplification
of total solar irradiance (TSI) variations by the addition
of energy
in cloud - free regions enhancing tropospheric circulation features (Meehl et al. 2008; Roy & Haigh 2010); numerous solar - related influences (including solar wind inputs) to the properties
of the global electric circuit (GEC) and associated microphysical cloud changes (Tinsley 2008).
Here, the authors use satellite and aircraft data to investigate the radiative impact
of volcanic
aerosols in the lowermost
stratosphere since the year 2000.
There is no obvious answer, unless you look to stratospheric
aerosol cooling —
in the
stratosphere, you'd need about 10 %
of the sulphates you'd require
in the troposphere for the same cooling effect.
As a test
of the models» annular sensitivity, the response to volcanic
aerosols in the
stratosphere is calculated during the winter following five major tropical eruptions.
In other words: Proposed strategies to alter the amount
of sunlight hitting the Earth's surface by (for example) deliberately injecting millions
of tons
of sulfate
aerosols into the
stratosphere pose enormous risks and uncertainties and don «t address the underlying causes
of global warming or other major risks from rising concentrations
of carbon dioxide, such as ocean acidification.
For instance, given the physics
of sulphate
aerosols in the
stratosphere (short wave reflectors, long wave absorbers), it would be surprising if putting
in the
aerosols seen during the Pinatubo eruption did not reduce the planetary temperature while warming the
stratosphere in the model.
Tinkering with the Earth and its atmosphere
in an attempt to fend off global warming — a.k.a. geoengineering — seems like the stuff
of science fiction: Lacing the
stratosphere with sulfur
aerosols or whitening clouds over the ocean to reflect sunlight back into space.
What does seem to be known is that
aerosols fall out
of the lower atmosphere (as high as they can be launched with conventional bombs)
in days, and persist for less than 2 years when launched into the
stratosphere by a major volcanic event like Pinatubo which was equivalent to several H bombs.
Until late
in the last century, widespread usage
of household and commercial
aerosols containing chlorofluorocarbons (CFC), unstable compounds which are carried into the
stratosphere, lead to significant and rapid ozone depletion.
The story revolves around a paper that Paul Crutzen (Nobel Prize winner for chemistry related to the CFC / ozone depletion link) has written about deliberately adding sulphate
aerosols in the
stratosphere to increase the albedo and cool the planet — analogous to the natural effects
of volcanoes.
If the major emitters
of greenhouse gases find it hard to agree on setting caps on emissions now, what makes you think the world can agree to injecting
aerosols in the
stratosphere as a solution?
During this period, the
aerosol amount varied with dust export from Africa, but also from major eruptions by two volcanoes (El Chichon
in 1982 and Pinatubo
in 1991), each
of which left a reflective layer
of sulfate droplets
in the lower
stratosphere for a couple
of years.
To elucidate human induced changes
of aerosol load and composition
in the atmosphere, a coupled
aerosol and gas - phase chemistry transport model
of the troposphere and lower
stratosphere has been used.
That cooling is a response to the decrease
in penetrating solar radiation caused by the «shading» effects
of aerosols spewed into the
stratosphere by the explosive volcano — not from a decrease
in manmade greenhouse gases.